This invention relates to perforating system in general and, more specifically, to a tubing conveyed well perforating system having an improved firing mechanism.
In completing well bores, it is desirable to use a large diameter casing-type gun to efficiently perforate the casing and form passageways which extend into the formation through which formation fluids may flow into the casing. In many instances where it is desired to perforate long intervals of the formation, a series of sequentially connected perforating guns are run into a cased well bore on the end of a tubing string. In some instances, it may be desirable to isolate the formation during the perforating operation to minimize contamination of the formation by fluids in the casing and to subject the formation to a reduced pressure (below formation pressure) to encourage the rapid flow of formation fluid into the casing, after perforation of the casing, to attempt to wash or clean the perforations.
To accomplish the isolation of the formation from the fluids in the casing the perforating guns may be sequentially connected below a packer having a perforated nipple connected to the bottom thereof. When the string of perforating guns is connected below a packer having a perforated nipple connected to the bottom thereof, since the pressure in the well bore below the packer may be reduced by the control of the level of fluid in the tubing string used to convey the packer and perforating gun, a large pressure differential may exist between the interior of the perforated casing and the formation surrounding the perforated casing which may facilitate the formation fluids flowing into the casing washing or cleaning the perforations.
In some instances, when using tubing conveyed perforating guns, it may be desired to use a sinker bar having a firing mechanism attached thereto to actuate the perforating guns. Typically, when using a sinker bar to actuate a string of perforating guns, detonation of the guns is usually accomplished from the top gun of the series when the sinker bar detonates a primer cord explosive in the top gun which, in turn, detonates the shaped charges in the perforating guns.
Examples of tubing conveyed perforating guns are shown in U.S. Pat. Nos. 2,169,559; 2,530,966; 2,745,495; 3,011,551; and 3,291,207 while examples of tubing conveyed perforating guns which are actuated through the use of sinker bars are shown in U.S. Pat. Nos. 2,456,977; 2,760,408; and 3,706,344.